Laminar flow burner head



Sept. 30, 1969 HELL LAM INAR FLOW BURNER HEAD Filed April 18, 1966 2 Sheets-Sheet 1 FIG. I

FIG. 3

FIG. 2

FIG. 4

INVENTOR.

AUGUST HELL. BY fl/{Mu FIGS ATTORNEY Sept. 30, 1969 A. HELL 3,469,794

LAMINAR FLOW BURNER HEAD Filed April 18. 1966 2 Sheets-Sheet 2 FIG. 6 FIG. 7a

FIG. 7c

INVENTOR.

AUGUST HELL BY /%/%M ATTORNEY United States Patent 3,469,794 LAMINAR FLOW BURNER HEAD August Hell, Whittier, Calif., assignor to Beckman Instruments, Inc., a corporation of Caiifornia Filed Apr. 18, 1966, Ser. No. 543,431 Int. Cl. 1305b 1/00, 1/14; A62c 31/02 US. Cl. 239-597 4 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a burner head particularly adapted for atomic absorption and flame photometry and useful with nitrous oxide-acetylene flames which comprises a head of substantial mass with a slot therein to provide laminar flow of the gases through said slot and a groove adjacent to the slot to provide a thin walled portion around the slot.

In my co-pending application, Ser. No. 339,218 for Burner System, filed Jan. 21, 1964, and assigned to the assignee of the instant invention, there is disclosed an improved laminar flow burner including a burner head having a narrow elongated slot formed therein. As disclosed in the aforementioned application the burner head is formed of heavy steel bars separated by a flat spacer to provide an elongated slot. The heavy steel bars conduct away heat and form a relatively cool slot which provides good quenching properties thus reducing accidental flashback hazards. One of the problems encountered with the nitrous oxide-acetylene flame are the carbon deposits which form along the slot which can impair the analytical accuracy and eventually clog the slot or generate serious flashback hazards. These carbon deposits have been found to form rapidly necessitating repeated and cumbersome shut-downs to clean the burner slot. Burner heads constructed after the teachings of this invention greatly deter or completely eliminate the formation of these carbon deposits.

FIG. 1 is a pictorial view of a conventional burner head which has been utilized with a nitrous oxide-acetylene flame illustrating heavy carbon deposits formed thereon;

FIGS. 2 and 3 are enlarged views of the carbon deposit taken from the burner of FIG. 1, FIG. 2 illustrating :a portion of the deposit adjacent the slot and FIG. 3 being a cross-section of the deposit;

FIG. 4 is a pictorial view of a burner head constructed according to the teachings of this invention along half of the slot length;

FIG. 5 is a side elevation of the burner head of FIG. 4;

FIG. 6 is a cross-section of the burner of FIGS. 4 and 5 taken along line 66; and

FIGS. 7a-7c are cross-sections of alternative embodiments of the invention.

Referring now to FIG. 1, the prior art burner head consists of two symmetrical pieces of heavy metal bars 10 and 11 having flat inner parallel walls and tapered outer walls. The symmetrical pieces are spaced apart by fiat spacers at each end thereof thereby forming an elongated 3,459,794 Patented Sept. 30, 1969 slot having a length 14 over the central portion thereof. The combustion supporting and fuel gases :are generally pre-mixed within the burner assembly and flow through and burn along the elongated slot. The symmetrical pieces or bars are held together by two screws 15 and 16. Holes 19, 20 and 21 are for screws which mount the burner head to the remaining portion of the burner assembly. Three holes, not shown, are also contained in bar 10. Alternatively, the burner head may be attached to the burner assembly by means of suit-able spring clips as more fully disclosed in my aforementioned co-pending application.

When the conventional prior art burner head is utilized with the nitrous oxide-acetylene flame, heavy carbon deposits form on either side of the slot as is illustrated at 22 in FIG. 1. The deposit in FIG. 1 was formed after approximately 15 minutes of use with the nitrous oxideacetylene flame and is approximately 0.1 inch high.

FIG. 2 illustrates a view of a portion of the deposit adjacent the slot, that is, bars 10 and 11 were separated and the deposit is viewed perpendicular to the slot surface. FIG. 3 is a cross-section of the deposit formed on one of the burner head bars of FIG. 1, i.e., is a cross-section perpendicular to the burner slot. The inner portion of the deposit adjacent the slot has the metallic appearance of graphite grown in crystalline form and a tree-like construction. The crystalline structure can also be seen at 30 in FIGS. 4 and 5. The outer layer of the deposit as seen in FIG. 1 and in the cross-sectional view of FIG. 3 has the amorphous, jet black appearance of carbon black.

Microscopic examinations show that the formation of these carbon deposits starts approximately 0.008 to 0.01 inch away from the edge of the slot. One of the purposes of the heavy metallic head bars is to prevent distortion of the slot assembly due to heating and to maintain a relatively cool slot by conducting heat away from the slot to aid in quenching the flame in the flashback direction. Although the reason for the formation and spacing of the carbon deposits is not fully understood it is suspected that there is a steep temperature gradient near the edge of the slot. That is, it is believed that immediately adjacent the slot the temperature of the bar is extremely high thereby preventing carbon deposits. As the temperature decreases across the bars, carbon adheres to the bars and the formation occurs.

FIGS. 4 and 5 illustrate a burner head constructed according to the prior art along half of its length and according to the teachings of this invention along the other half. Referring to FIG. 6 which illustrates a crosssection of the novel slot design taken along line 6-6 of FIG. 5, a groove 25 is machined parallel to the slot in such a way as to leave a thin upstanding slot edge or rim 28 and 29. The slot is also machined around the end portion of the slot as is best illustrated in FIG. 4. In the particular embodiment the groove was approximately 0.08 inch deep and the upstanding rim has a width of approximately 0.005 to 0.007 inch thick. In the particular burner head of FIGS. 4 and 5 the rear rim 28 was kept slightly thicker than the front rim 29. It may be seen that while a substantial build-up of carbon occurred along the conventionally constructed right half of the slot, there is substantially no carbon formation on the thinner front rim of the slot while the carbon formation on the thicker rear rim has been greatly retarded, being limited to a few crystalline-like formations. The burner head of FIGS. 4 and 5 was utilized with the nitrous oxide-acetylene flame for approximately 15 sulting in higher temperatures at the slot edge and retarding the carbon formation. Furthermore, the physical configuration of the slot edge, i.e., the thin construction thereof, makes adherence of the carbon at the slot edge difficult and reduces the mechanical strength of any deposit build-up. Still further, because of the indentation created in the bars by the milled slot, deposits on the bar where the temperature gradient would allow such deposit to adhere are retracted from the base of the flame. Although for the purposes of illustration the rear rim of the slot was made slightly thicker than the front rim in FIGS. 4 and 5, in practice it would be more usual to maintain the rims substantially the same thickness.

The groove formed in the bars does not necessarily have to be rectangular as illustrated in FIG. 6. FIGS. 7a, 7b, and 7:: illustrate alternative cross-sections of burners constructed after the teachings of this invention which also provide for the retardation or elimination of the carbon deposits. In FIG. 7a the groove is of angular shape with a flat-top edge for the rim. FIG. 7b illustrates substantially the same cross-section except the rim is formed with a sharp edge. The configuration of 7a has some advantages over that of 7b in that it is extremely difficult to machine a narrow groove having a sharp edge as illustrated in 7b because of the mechanical deformation of the main surface of the slot assembly. Such deformation may cause undesired non-uniformities in the flame.

The depth, width and configuration of the groove are not critical although a depth of 0.05 to 0.08 inch with a rim edge of not greater than 0.007 to 0.008 inch appears to eliminate the formation of any deposits. However, any approach which prevents a steep lateral temperature gradient at the slot edge or which provides a sharp rim at the top of the slot edge, or a combination of both, which completely or substantially eliminates the formation of carbon deposits along the burner slot may be utilized.

There has been illustrated and described a new and improved burner head for laminar flow burners particularly adapted for the elimination of carbon deposits when utilized with a nitrous oxide-acetylene flame and various alternative embodiments thereof. It should be understood that various changes can be made in form, details and arrangements and proportions of the various parts by those skilled in the art.

What is claimed is:

1. In a burner head for use in a burner system for the analysis of elements comprising a head member having an elongated slot formed therein to provide laminar flow of combustion gases therethrough and a groove formed adjacent said slot.

2. In a burner head for use in a burner system for the analysis of elements, said head composed of heavy metal having a slot formed therein by fiat inner parallel walls to provide laminar flow of gases therethrough the improvement comprising a thin walled portion adjacent said slot formed by a groove around said slot.

3. The burner of claim 2 wherein said thin walled portion is substantially even with the outer main surface of said head.

4. The burner head of claim 2 wherein said thin walled portion is recessed below the outer main surface of said head.

References (Iited UNITED STATES PATENTS 2,755,137 7/1956 Hughf 239-597 XR 3,054,563 9/ 1962 Steinen 239597 XR FOREIGN PATENTS 1,043,616 7/1953 France.

M. HENSON WOOD, JR., Primary Examiner BERNARD BELKIN, Assistant Examiner US. Cl. X.R. 239568, 601

Po-ww UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,469 ,794 Dated September 30 1969 Inventor(s) August l It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 69, "of" should read or.

SiGNED ANu SEALED DE: 2 3 15m (SEAL) Attest:

EdwardMFlewh r. J WILLIAM E. SOHUYIER, .m. Attesting Officer Gamissioner of Patents 

